1. Field of the Invention
This invention relates generally to offshore pipelines, and more specifically to a pipe joint weld collar covering for the contiguous end portions of a pair of pipes of an oil or gas pipeline joined together by a metal weld, and method of installation of the collar.
2. Description of the Prior Art
The high world-wide demand for energy in the form of oil and gas and the limited supply thereof has led to greatly increased offshore drilling activities in many countries. To transport the oil and gas from the undersea wells to refineries, a vast network of sea bed pipelines is required. The pipelines are formed from forty foot lengths of pipe which are joined together by welding on a lay barge and then fed onto the ocean floor.
Each forty foot length of pipe goes through many steps before it is transported to the lay barge. The manufactured pipe, preferably a seamless pipe of superior alloy material, is cleaned, then corrosion controlled coatings are applied to the outer pipe surface, and then a coating of high specific gravity material, such as concrete is applied to the outer surface of the pipe. The coating is applied to prevent the pipeline from floating to the surface when raw materials of a density less than water are transported therethrough. This coating may vary anywhere from one to six inches of thickness, depending on requirements. All of the aforementioned steps are performed on the entire outer surface of each forty foot length of pipe except for the last eight to twelve inches on each end thereof. These recessed end areas, referred to in the industry as cutback areas, are left free of coating material to provide access to the pipes so that one end of one pipe may be joined by welding to one end of an adjacent pipe on the barge. On the lay barge, the lengths of pipe pass through a series of stations before they become part of the pipeline. A length of pipe is aligned with and tack welded to an adjacent length of pipe at the first station, and finish welding is accomplished at subsequent stations in the operation. The welds are tested at another station by x-rays or the like, and if found defective, are redone at the testing station. The welded area is then cleaned, one of many forms of corrosion barrier is applied to the welded area, and the pipes advanced to the joint filling station, where the recess or cutback areas of the pipeline are covered to protect the weld and corrosion barrier from damage. This is achieved by filling the annular recess or cutback area, which varies from 16-24 inches (40.48-60.96 cm) in length by 1-6 inches (2.53-15.18 cm) in thickness, with various materials. This enables the pipeline surface to pass over the rollers at the transom of the lay barge as the pipeline is fed onto the sea or ocean floor. If the tensioned line were to snag on a roller, due to an indentation at the recess or cutback portion, the roller could be severely damaged and cause barge delay for repair. Furthermore, if the line were to surge after being snagged, it could cause a buckle which has been known to travel down the pipeline until it reaches the bottom. This can cause the loss of a mile or more of expensive pipe and add to the barge delay time. Also, if the annular recess or cutback portion is not protected, the corrosion coatings stand a high risk of being damaged, which can jeopardize the life of the entire pipeline.
Known methods in the industry for allowing the pipeline to make a smooth transition over the lay barge pipe rollers onto the sea floor, and for protecting the pipe joint from damage once the pipeline is on the sea floor involve filling the annular recess or cutback area surrounding the welded pipe joint with a quick setting material, such as a marine mastic, a polyurethane foam or different concretes. The most prevalent system or method being used today is the marine mastic method. This method comprises chopping mixed blocks of mastic (tar) and aggregate (gravel), and transporting the chopped product into a fuel fired kettle for melting. The resulting viscous material is poured into a permanent sheet metal mold banded around the annular recess or cutback area to be filled. This marine mastic method of filling the annular recess suffers from a great number of disadvantages and problems. For example, it is labor intensive requiring seven to eight men per shift. Another problem is that the method involves the use of flammable materials resulting in an increased health risk to personnel, risk of damage to the barge and an increased insurance cost. Other problems are that the marine mastic has a long set time, and is incompatible with some corrosion coatings, and especially to shrink sleeves. Another problem is that the marine mastic method involves expensive machinery. Still another problem presented by the marine mastic method is that it exposes the personnel to hazardous fumes and pollutants. Still other problems of the marine mastic method are that extra fuel for the melting kettles, and a large amount of barge space for machinery and raw materials are required. Another problem of the marine mastic method is that no inspection is possible for complete filling of the annular recess. Still another problem of the marine mastic method is that the deteriorating sheet metal molds at the bottom of the water are hazardous to nets of the local fishing industry. Also, a pipe joint recess filled with the marine mastic offers only fair impact resistance and is an expensive system.
The polyurethane foam method is gaining increased acceptance in the industry due to the fact that it is slightly less expensive than the marine mastic method and more convenient to use. The polyurethane foam method is similar to the marine mastic method, in that the two part material is mixed and injected into a permanent, banded metal mold. Disadvantages or problems presented by the polyurethane foam method are: (1) it is labor intensive (four to five men per shift), (2) large expensive equipment is required that is prone to mechanical failure (barge delay), (3) the polyurethane foam material is temperature sensitive, (4) skilled mechanics are required, (5) the polyurethane foam material is bouyant thereby reducing the weight of the pipeline, (6) the polyurethane foam has a low impact resistance, (7) deteriorating metal molds are hazardous to nets of the local fishing industries, and (8) the polyurethane foam method is an expensive method.
The recess filling method involving different concretes has met with little success in the industry. This method, involving polymer cements and quick-set concretes, has many of the above disadvantages and problems recited for the marine mastic and the polyurethane foam methods. However, the primary disadvantage or problem presented by the cement and concrete methods is that it is extremely expensive.
In light of the many problems and disadvantages inherent in and presented by the aforementioned known and described methods, an improved simple, more reliable and cost-effective method for filling the annular recess or cutback area surrounding the pipe weld joint is desparately needed. The pipe joint weld collar of this invention fulfills this need by effectively solving the aforementioned problems presented by the known methods.